Large scale earth excavation operations are typically performed using a powered excavating apparatus, such as a tracked excavator, having an articulated, hydraulically pivotable boom structure with an elongated, pivotal outer end portion commonly referred to as a “stick.” Secured to the outer end of the stick is an excavating bucket which is hydraulically pivotable relative to the stick between “closed” and “open” positions. By pivotally manipulating the stick, with the bucket swung to a selected operating position, the excavator operator uses the bucket to forcibly dig into the ground, scoop up a quantity of dirt, and move the scooped up dirt quantity to another location, such as into the bed of an appropriately positioned dump truck.
A common occurrence during this conventional digging operation is that the bucket strikes refusal material (in excavation parlance, a material which “refuses” to be dug up) such as rock which simply cannot be broken and scooped up by the bucket. When this occurs it is typical practice to stop the digging operation, remove the bucket from the stick, and install a hydraulically operated “breaker” on the outer end of the stick in place of the removed bucket. The breaker has, on its outer end, an oscillating tool portion which rapidly hammers the refusal material in a manner breaking it up into portions which can be subsequently dug up. After the breaker has been utilized to break up the refusal material, the operator removes the breaker from the stick, replaces the breaker with the previously removed bucket, and resumes the digging operation with the bucket.
While this procedure is easy to describe, it is a difficult, laborious and time-consuming task for the operator to actually carry out due to the great size and weight of both the bucket and breaker which must be attached to and then removed from the stick, and the necessity for the operator to climb into and out of the high cab area of the excavator (often in inclement weather) to effect each bucket and breaker change-out on the stick. This sequence of bucket/breaker/bucket change-out, of course, must be laboriously repeated each time a significant refusal area is encountered in the overall digging process.
A previously utilized alternative to this single excavator sequence is to simply provide two excavators for each digging project—one excavator having a bucket attached to its boom stick, and the second excavator having a breaker attached to its boom stick. When the bucket-equipped excavator encounters refusal material during the digging process, it is simply moved away from the digging site, and the operator climbs down from the bucket-equipped excavator, walks over to and climbs up into the breaker-equipped excavator, drives the breaker-equipped excavator to the digging site, and breaks up the encountered refusal material. Reversing the process, the operator then switches to the bucket-equipped excavator and resumes the digging process to scoop up the now broken-up refusal material.
While this digging/breaking technique is easier on the operator, it is necessary to dedicate two large and costly excavators to a given digging task, thereby substantially increasing the total cost of a given excavation task. A modification of this technique is to use two operators—one to operate the bucket-equipped excavator, and one to operate the breaker-equipped excavator. This, of course, undesirably increases both the manpower and equipment cost for a given excavation project.
Another attempt to solve this problem is disclosed in U.S. Pat. No. 6,085,446 and U.S. Pat. No. 4,100,688 for an excavating machine having a motorized milling tool attached to the back of the bucket. A primary disadvantage of these devices is complexity, cost, and reliability. Another disadvantage is the weight that must be continuously carried by the bucket. The additional weight substantially reduces the carrying capacity and mobility of the bucket. Another disadvantage to the device of U.S. Pat. No. 6,085,446 is that the back of the bucket cannot be used to smooth or pad the soil, as is a well-known practice in the industry. Another disadvantage is that surface rock is not subject to an overburden pressure, so it generally fails faster under compression and impact forces than by the shearing forces of a scraping and gouging rotary drilling tool.
Another attempt to solve this problem is disclosed in U.S. Pat. No. 4,070,772 for an excavating machine having a hydraulic breaker housed inside, or on top of, the boom stick. A primary disadvantage of this device is that it is extremely complex and expensive. Another disadvantage of this device is that it cannot be retrofit to existing excavators. Another disadvantage of this device is that the size of the breaker is limited. Another disadvantage of this device is that the bucket must be fully stowed to access the breaker and vice versa, making simultaneous operation impractical.
Another attempt to solve this problem is disclosed in U.S. Pat. No. 5,689,905 for another excavating machine having a hydraulic breaker housed inside, or on top of, the boom stick. In this device, the chisel portion of the breaker is removed when not in use. A primary disadvantage of this device is that it fails to permit immediate, unassisted switching from breaker to bucket, and thus simultaneous operation is impossible. Another disadvantage of this device is that it requires manual handling of the extremely heavy chisel tool each time the operator desires to convert to a breaker or bucket operation. Another disadvantage of this device is that it is extremely complex and expensive. Another disadvantage of this device is that it cannot be retrofit to existing excavators.
A more recent attempt to solve this problem is disclosed in U.S. Pat. No. 6,751,896 for an excavating machine having a boom stick portion on which both an excavating bucket and a hydraulic breaker are mounted for hydraulically driven pivotal movement between first and second positions. A deployment system is disclosed having a bracket for closely aligned pivotal support of both the breaker and a single hydraulic cylinder on a single bracket. While this design is a marked improvement over the prior art, its primary disadvantage is that it lacks the desired level of durability at the first pivot and extension limiting (stop) mechanisms to tolerate the massive reciprocating loads of operation over time. Another disadvantage is that it is difficult to disassemble the first pivot to replace tool components. Another disadvantage is that the means for lubricating the bearing surface of the first pivot was ineffective and weakened the first pivot assembly. Another disadvantage is that it suffers durability loss from exposure of mechanical fasteners to the excavated material.
As can be readily appreciated from the foregoing, a need exists for an improved design for carrying out the requisite digging and refusal material-breaking portions of an overall excavation operation in a manner eliminating or at least substantially eliminating the above-mentioned problems, limitations and disadvantages commonly associated with conventional digging and breaking operations. It is to this need that the present invention is directed. In particular, there is a need for a new design with superior durability to the designs disclosed in U.S. Pat. No. 6,751,896.